One Answer:

In general, stomach sleepers need a mattress that is less soft than other sleepers. Side sleepers tend to need the most softness, and back sleepers are in the middle (and are also the most adaptable to different levels of softness).

To blend the needs of a stomach sleeper and a back sleeper, you are going to be looking at mattresses that are on the firmer side of the spectrum. Within that range though, the right choice will come down to other factors.

In terms of fit, this mattress (the Sealy Willow Firm) is on the firmer side of the spectrum, which is good. However that does not mean it will provide proper spinal alignment and pressure relief for you and your spouse, which will depend on other factors such as your weight and age. In addition, fit is also a function of other factors, like its ability to meet your preferences regarding motion isolation, cushioning depth, "memory" feel, natural materials, temperature, etc.